Make a Low-Poly Object with an equal balanced number of Vertices
For redistributing the verts try the remesh modifier. 

To make your model look more like the picture you posted, you have to lower your polycount, which you can do by editing parameters in the remesh modifier I mentioned or by retopologizing manually.

As for good low poly modeling, there are plenty of tutorials, and that's not something I can answer here. It'll take practice and patience, as low poly is harder than it looks.

For texturing, since it's done on a face-by-face basis, do not use UVs or textures, but instead use multiple materials and assign different materials to different faces.

Lighting like that is decently simple. Flat shading, a directional light, and some global illumination. If you're using Unity, also look into the image effects standard assets, like screen space ambient occlusion or color correction. After that, just iterate.